In recent years, hybrid vehicles powered by an engine and a motor have become popular due to environmental requirements such as low fuel consumption and low exhaust gas emission. Hybrid vehicles may have several driving modes from which to switch between including (i) an engine travel mode, in which the vehicle travels on a drive power from an engine, (ii) an EV travel mode, in which the vehicle travels on a drive power from a motor generator, (iii) an MG assist mode, in which the vehicle travels on a driver power from both of the engine and the motor generator, and (iv) an engine generation mode, in which the engine is driven to a more-than-required level, i.e., to drive both of the vehicle and the motor generator, which is used for generating electricity.
For example, in a patent document 1 (i.e., Japanese Patent Document No. 3901235), the start and stop of the engine are switched according to a depression amount of an accelerator pedal or a brake pedal.
However, the system in patent document 1 does not take an efficiency of the engine into account, for example. As a result, such a switching scheme of the drive modes may not necessarily yield the best result in terms of fuel efficiency and other factors.
Further, for example, in a patent document 2 (i.e., Japanese Patent Laid-Open No. JP-2007-176270A), an operation of the motor generator for generating electricity and an operation of the motor generator for driving the vehicle are compared with each other, in order to determine which one of those two operations creates greater economic benefits than the other. Then, based on a comparison result, an instruction command for operating the motor generator in a more economic mode is sent to the motor generator.
However, the patent document 2 is silent about the economic benefits of the EV travel mode in which the vehicle travels only on drive power from the motor generator but not drive power from the engine.